A noise dosimeter is a device which incorporates a sound level measurement subsystem and a methodology for accumulating the sound level over time. ANSI S.125-1991 is the American National Standard Specification for Personal Noise Dosimeters, a comprehensive standard that describes how a standard noise dosimeter should function. The result of noise dosimeter integration may be what is known as the “equivalent continuous sound level”, denoted as Leq. A noise dose might also be expressed as a percentage of “criterion exposure.” In terms of Pascals (the mks standard unit of sound pressure, the Pascal (Pa)), the criterion exposure recommended as safe in NIOSH-1998 is a maximum of 3640 Pa2s per day. Where s denotes the time in seconds and Pa2 is the instantaneous power. The “criterion sound level” is the level of sound, which continuously applied for eight hours results in 100% criterion exposure. A Sound Pressure Level of 85 dB SPLA will produce 3640 Pa2s at the end of eight hours. These calculations are completely specified in the standard and are well known in the industry.
Many environments expose individuals to excessively loud sounds. These loud sounds include, for example, music concerts, industrial manufacturing environments, construction and environments involving the use of heavy machinery, etc. The US government regulates, through OSHA (Occupational Safety and Health Administration), noise exposure levels in work environments. There are many noise dosimeters on the market, which are used to monitor noise in the work environment. These regulations and devices represent a level of protection for many American workers.
Additionally, with the increased use of personal audio players with earphones such as iPods and other portable audio devices, and earphones in general (in a plane, watching a movie with the sound of the engine in the background) the exposure to noise is drastically greater. To be able to hear their music in a noisy environment, listeners may increase the volumes of their music or movies to levels that can be damaging to their hearing without realizing the dangers associated with the loud sounds in their ears. For example, in an aircraft cabin, the noise levels tend to be 75-80 dBA SPL, which often induce passengers to increase the volume in their open-ear airline earphones to levels of 85-95 dBA SPL. A level of 91 dB for 4 hours exceeds by 200% the recommended daily exposure using NIOSH-1998 recommended criteria. Noise-excluding earphones help reduce risk, but a few listeners appear to have become addicted to loud sounds. (Florentine et al., Ear & Hearing 1998; 19; 420-428).
Applicant has found that live orchestral music such as, for example, that heard in an Orchestra Hall when the Chicago Symphony Orchestra is playing a piece such as Stravinski's Rite of Spring or Berlios' Damnation of Foust, can produce a sound pressure level (SPL) of 102 to 104 dB at an audience seat in the first balcony of Chicago's Orchestra Hall. An earphone that can accurately reproduce such music, must have an undistorted output capability of 115 dB SPL (referred to the sound field equivalent) measured with sine-wave signals. That same earphone can cause hearing damage if listened to at full volume while playing music that tends to stay at the same level all the time. Unfortunately, listeners often do not know when their ears are at risk. The need for a personal device that alerts a user when noise surpasses a recommended safe level is therefore becoming a necessity.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.